This invention relates to the field of balancing assistance for persons who are deprived of the sense of touch in one or both legs. Such deprivation may be due to the loss of a limb or may be the result of spinal cord injury. In either case the disabled person lacks information which is fundamental to the maintenance of vertical balance during standing or walking. Obviously the condition is much more severe for a person afflicted with spinal cord injury, because the damage affects both legs, as well as the entire body trunk below the level of the spinal cord injury. Thus, this invention is particularly applicable to the field of balancing assistance for spinal-cord-injured persons.
It is well known that a spinal cord injury breaks the communication link between the brain and the affected muscles, but the muscles themselves are otherwise undamaged. Thus, it has been found that useful movement of the muscles may be restored through functional electrical stimulation. Typical systems for performing such stimulation are disclosed in Petrofsky et al. U.S. Pat. No. 4,499,900 and in Petrofsky et al. U.S. Pat. No. 4,456,214, both of which deal with therapeutic exercise for leg muscles.
The systems disclosed in the above noted Petrofsky et al. patents include sensors which measure leg motion and feedback loops which are connected to a microprocessor. The microprocessor compares a measured movement to a desired movement and generates appropriate stimulation control signals. The stimulation control signals are applied to stimulation electrodes which are positioned for stimulating controlled contractions in target muscles.
Electrically stimulated walking is also feasible as disclosed in Petrofsky et al. U.S. Pat. No. 4,569,352. However, stimulated walking is a much more complex operation than simple stimulated leg exercising. As shown in Petrofsky et al. No. '352, stimulated walking may require coordinated, closed loop control of as many as ten muscle groups. Additionally, leg braces are required in order to avoid the necessity of stimulating even more muscle groups. The control problem is further complicated by the requirement to maintain a delicate vertical balance. The disabled person typically provides balancing control through the use of canes or a suitable walker. As taught in Petrofsky et al. No. '352, ON/OFF floor contact switches may be provided at the heels and toes of the disabled person. Information from these switches is provided to the microprocessor, but this does not contribute very much to balancing control.
It is also possible for a spinal cord injured person to achieve a certain degree of ambulation without functional electrical stimulation. This may be accomplished through use of a reciprocation-gait orthosis as disclosed in an article entitled "The LSU Reciprocation-Gait Orthosis" by Douglas et al., Orthopedics July, 1983, pages 834 through 839. This orthosis utilizes leg braces which are locked at the knees and hip joints which are interconnected by a pair of cables. Cable connections are made in such a fashion that extension of either hip produces flexion of the opposite hip. Balancing is achieved through a suitable walker.
A significant simplification of electrically stimulated walking may be achieved by combining stimulation with a reciprocation-gait orthosis, as described in a paper entitled "Computer Synthesized Walking, An Application of Orthosis and Functional Electrical Stimulation (FES) " by Petrofsky et al., The Journal of Neurological & Orthopaedic Medicine & Surgery, Vol. 6, Issue 3, October, 1985, pages 219 through 230. As with the other above described systems, a stable center of gravity must be maintained. Again, this is supplied by the disabled person through the use of canes or a walker.
In order for a human being to maintain an erect position during standing or walking it is necessary for the brain to receive some type of cognitive feedback. Heretofore the only cognitive feedback available to the spinal-cord-injured person has been provided by the sense of vision. Generally speaking the person looks down toward the floor, visually determines the sequence of walking and adjusts the upper body accordingly. Although this may be satisfactory in a controlled laboratory setting, it is not practical for routine walking in various environments. The visual sense of the person must be unrestricted for use in other activities.
Accordingly, there is a need to provide balancing assistance apparatus and method for use by persons who have been deprived of the sense of touch in one or both legs. Preferably, such apparatus and method should provide balancing information as cognitive feedback flowing directly to the disabled person without the intervention of a computer. Also, it is desirable that the balancing assistance operate in a stimulated or non-stimulated environment and function effectively both for walking and standing.